1. Field of the Invention
The present invention relates to a display device, and more particularly, to a sharpness improvement apparatus for analogue videos signals to display a clear image in a display device such as a television receiver and a monitor.
2. Description of the Background Art
Generally, a display device such as a television receiver and a monitor can not realize a clear image when an image signal of a received signal or an analogue image signal inputted from a computer system is processed into a predetermined analogue such as an amplification and a conversion because an edge characteristic of the image signal is deteriorated.
FIG. 1 is a block diagram showing a display device to which a sharpness improvement apparatus according to the conventional art is applied. The display device comprises an image source processing unit 110 for performing a predetermined image process by receiving an image signal; an analogue image processing unit 130 for outputting R, G, and B signals which can be displayed by receiving the signal processed in the image source processing unit; an analogue sharpness improvement unit 150 for improving a sharpness of the R, G, and B signals by receiving the R, G, and B signals; and a display unit 170 for receiving the R, G, and B signals having an improved sharpness and displaying them on a screen.
Operations of the display device will be explained as follows.
First, the image source processing unit 110 receives a predetermined image signal from an image media (not shown) connected to the outside or the inside or a storage media (not shown) and processes the image signal. Then, the analogue image processing unit 130 receives the signal-processed image signal, converts into the R, G, and B signals, and outputs. At this time, since the analogue image processing unit 130 is generally used by analogue devices, the R, G, and B signals are degraded than an original image source. Accordingly, the degraded R, G, and B signals have to be displayed on a screen of the display unit 170 by being improved in the analogue sharpness improve unit 150.
At this time, in case that a predetermined image signal is ideally processed in the analogue image processing unit 130, a gradient of one pixel signal is very sharp as shown in FIG. 2A. However, as shown in FIG. 2B, if the predetermined image signal is substantially processed in the analogue image processing unit 130, the gradient of the one pixel signal is very dilatory.
Accordingly, the image signal processed in the analogue image processing unit 130 is degraded and the gradient becomes dilatory. In case that the image signals are displayed in the display unit 170, as shown in FIG. 3, edges of left and right sides adjacent to a region where an image of the display unit is displayed are not clear compared with edges of the displayed screen.
Hereinafter, the analogue sharpness improvement apparatus 150 according to the conventional art will be explained.
FIG. 4 is a circuit diagram of the analogue sharpness improvement apparatus according to the conventional art. As shown, the sharpness improvement apparatus 150 comprises a first delay unit 151 for delaying the R, G, and B signals for a determined time by receiving them; a subtracter 152 for subtracting the delayed R, G, and B signals from the R, G, and B signals; a second delay unit 153 for delaying the delayed signal for a predetermined time; an AND operator 154 for AND operating the subtracted signal and the delayed signal from the second delay unit 153; an inverter 155 for inverting a signal outputted from the AND operator 154; a buffer 156 for synchronizing output time of the signals outputted from the AND operator 154 and the inverter 155; an amplifier 153 for amplifying the output signal of the AND operator 154 as a predetermined multiple; a differentiator 159 for differentiating the amplified signal; a Schmidt-trigger type buffer 160 for changing the differentiated signal into a square wave by a predetermined level; and a switching unit 157 for receiving a signal outputted from the Schmidt-trigger type buffer 160 and then selectively outputting.
The sharpness improvement apparatus according to the conventional art will be explained with reference to the attached FIGS. 5A to 5J.
First, as shown in FIG. 5A, when the predetermined R, G, and B signals are inputted to the first delay unit 151 and the subtracter 152, the first delay unit 151 outputs a signal delayed as a predetermined time as shown in FIG. 5B. Then, the subtracter 152 subtracts the delayed signal from the R, G, and B signals and then outputs as shown in FIG. 5C.
The second delay unit 153 delays the subtracted signal for a predetermined time as shown in FIG. 5D and then inputs to the AND operator 154. Then, the AND operator 154 logically multiplies a signal subtracted from the subtracter 152 with a signal delayed from the second delay unit 153 and then outputs as shown in FIG. 5E. At this time, the signal of FIG. 5E is equal to a result that first-inputted R, G, and B signals are first differentiated.
Subsequently, the inverter 155 receives a signal outputted form the AND operator, inverts like FIG. 5F, and inputs to the switching unit 157. Also, the buffer 156 receives a signal outputted from the AND operator 154, passes as it is like FIG. 5G, and inputs to the switching unit 157.
Also, the amplifier 158 receives a signal outputted form the AND operator 154, amplifies into a predetermined multiple, and inputs to the differentiator 159. Then, the differentiator 159 differentiates the amplified signal and outputs to the Schmidt-trigger type buffer 160 as shown in FIG. 5H. Also, the Schmidt-trigger type buffer 160 receives the differentiated signal, changes it into a square wave by a predetermined level, outputs as shown in FIG. 5I, and inputs to the switching unit 157.
The switching unit 157 performs a predetermined switching according to a signal outputted from the Schmidt-trigger type buffer 160. That is, if the output signal of the Schmidt-trigger type buffer 160 is a potential more than a predetermined reference, an output signal of the buffer 156 is selected to be outputted during the duration, and if the output signal is a potential less than a predetermined reference, an output signal of the inverter 155 is selected to be outputted during the duration. Accordingly, the output signal of the switching unit 157 outputs the first-inputted R, G, and B signals by a second differentiation, and represents as a waveform of FIG. 5J.
The second differentiated R, G, and B signals have gradient characteristics improved approximately two times than the inputted R, G, and B signals, thereby improving sharpness of the inputted R, G, and B signals.
However, the sharpness improving apparatus 150 according to the conventional art can improve the sharpness of the inputted R, G, and B signals by outputting the second differentiated signal like the FIG. 5J only when it is ideally realized. Also, since the sharpness improving apparatuses 150 are all composed of analogue devices, a wanted second differentiation signal can not be precisely obtained.
Besides, since the sharpness improving apparatus according to the conventional art performs the first and second differentiation of the inputted R, G, and B signals by using the analogue devices, overshooting and undershooting are generated. According to this, the inputted R, G, and B signals have a ringing phenomenon by the overshooting and the undershooting. Therefore, edges of an actual screen are seen as black.
In addition, even though the sharpness improvement can be done softly so as to reduce the ringing phenomenon, said method has a limitation to achieve the sharpness improvement of the inputted R, G, and B signals as wanted.